remain in the hospital tonight in boston. we begin with the investigation. our own pete williams has been on it from the start. pete, good evening. >>> brian, after sifting through that huge amount of photos and video from people and businesses, the fbi wants to now know about two people who stand out in all that material because of what they were doing before the bombs went off. investigators tonight are calling them suspects in the bombings investigators decided today to take advantage of one of their strongest leads, asking for public help in identifying two men agents are now the most interested in running down. >> we consider them to be armed and extremely dangerous. no one should approach them. no one should attempt to apprehend them except law enforcement. >> reporter: one man is wearing a white baseball cap worn backwards, dark t-shirt, gray hoodie, dark jacket, dark pants
detonated here in boston. nbc's pete williams has been following the investigation in d.c. all day. pete, good evening. >> brian, good evening. still so many questions, but one has been answered, how many explosive devices were left at the scene. that answer is two. and officials describe them as crudely made but effectively used. and as of tonight, no suspects, no idea who did it or why. >> reporter: investigators have begun the process of recovering tiny pieces of the bombs to learn how they were made.
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